Method for forming a matrix composite layer and workpiece with a matrix composite layer

ABSTRACT

A method for forming a matrix composite layer on a workpiece and a workpiece with a matrix composite layer are disclosed. In an embodiment the method includes forming a wall around a metallic surface such that the wall extends in a vertical direction from a plane formed by the metallic surface, and depositing a filler material in a walled area on the metallic surface. The method further includes depositing a plastic material on the filler material and performing a vacuum treatment of the filler material and the plastic material thereby forming a matrix composite layer disposed on the metallic surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/486,907, filed on Apr. 13, 2017, which application is herebyincorporated by reference herein.

TECHNICAL FIELD

This disclosure in general relates to a semiconductor component and amethod for producing a semiconductor component, in particular asemiconductor component comprising means for attaching the semiconductorcomponent to a heat sink.

BACKGROUND

Semiconductor components are usually packaged and then mounted to aprinted circuit board. The semiconductor components may further becoupled to a heat sink, wherein the heat sink is configured to dissipateheat produced by the semiconductor component. Several different ways areknown of how a semiconductor component may be mounted to a heat sink.Such mounting methods, however, are often expensive, require a lot ofspace, and require one or more additional process steps for mounting thecomponent to the heat sink. There is a need to provide a semiconductorcomponent that may be easily mounted to another component, such as aheat sink, at reduced costs and with reduced effort.

SUMMARY

One example relates to a method. The method includes forming a firstthermally conductive layer on an outer surface of a semiconductorpackage. The first thermally conductive layer formed on the outersurface of the semiconductor package is configured to be mounted to anexternal heat sink.

Another example relates to a semiconductor component. The semiconductorcomponent includes a semiconductor package with an outer surface and afirst thermally conductive layer arranged on the outer surface of thesemiconductor package. The semiconductor component with the firstthermally conductive layer arranged thereon is configured to be mountedto an external heat sink such that the first thermally conductive layerfaces the heat sink.

Embodiments of the invention disclose a method comprising forming a wallaround a metallic surface such that the wall extends in a verticaldirection from a plane formed by the metallic surface of a workpiece,depositing a filler material in a walled area on the metallic surface,depositing a plastic material on the filler material and performing avacuum treatment of the filler material and the plastic material therebyforming a matrix composite layer disposed on the metallic surface.

Other embodiment of the invention disclose a method comprising clampingsidewalls of a workpiece with a clamper, depositing a filler material ona metallic surface of the workpiece, depositing a plastic material onthe filler material and performing a vacuum treatment of the fillermaterial and the plastic material thereby forming a matrix compositelayer disposed on the metallic surface.

Further embodiments of the invention disclose an arrangement comprisinga heatsink with a roughened metallic surface and a matrix compositelayer disposed on the roughened metallic surface, wherein the matrixcomposite layer comprises a ceramic filler material and a plasticmaterial, and wherein the ceramic filler material includes two or threedimensional particles, platelets, agglomerated particles or acombination thereof.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and onviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples are explained below with reference to the drawings. Thedrawings serve to illustrate certain principles, so that only aspectsnecessary for understanding these principles are illustrated. Thedrawings are not to scale. In the drawings the same reference charactersdenote like features.

FIG. 1 schematically illustrates a side view of a semiconductorcomponent that is mounted to a heat sink;

FIG. 2 schematically illustrates a top view of the semiconductorcomponent and heat sink of FIG. 1;

FIG. 3 schematically illustrates a side view of a semiconductorcomponent that is mountable to a heat sink by means of a screw;

FIG. 4 schematically illustrates a semiconductor component that ismounted to a heat sink by means of direct copper bonding;

FIG. 5 schematically illustrates a side view of an example embodiment ofa semiconductor component that is configured to be mounted to a heatsink;

FIG. 6 schematically illustrates a method for producing a semiconductorcomponent according to one example of the present invention;

FIG. 7 exemplarily illustrates an arrangement for electrophoreticdeposition.

FIG. 8 schematically illustrates one example of an electrophoreticdeposition process;

FIG. 9 schematically illustrates an example of a dispensing process;

FIG. 10, including FIGS. 10A-10C, schematically illustrates one exampleof a method for producing a semiconductor component;

FIG. 11 schematically illustrates a semiconductor component according toone example;

FIG. 12 (FIGS. 12A-12G) shows a method for forming a matrix compositelayer on a heat sink according to an embodiment;

FIG. 13 (FIGS. 13A-13G) shows a method for forming a matrix compositelayer on a heat sink according to another embodiment.

FIG. 14 (FIGS. 14A-14E) shows a method for forming a matrix compositelayer on a heat sink according to yet another embodiment; and

FIGS. 15A-15D show different types of filler materials in the matrixcomposite layer disposed on the heat sink.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings. The drawings form a part of the description andby way of illustration show specific embodiments in which the inventionmay be practiced. It is to be understood that the features of thevarious embodiments described herein may be combined with each other,unless specifically noted otherwise.

Several methods are known for mounting a semiconductor component to asecond component such as a heat sink, for example. Attachingsemiconductor components to heat sinks removes the waste heat that isgenerated during operation of the semiconductor components. FIG. 1 showsone known possibility for attaching a semiconductor component 100 to aheat sink 111. The semiconductor component 100 comprises a package 110.One or more semiconductor dies (not illustrated in FIG. 1) may bearranged within the semiconductor package 110. The package 110 maycomprise one or more pins or leads 113 for mounting the semiconductorcomponent 100 to a printed circuit board 200 and for providing anelectrical connection between the semiconductor die(s) in the package110 and the surrounding circuitry (e.g., on the printed circuit board200). The semiconductor component 100 is further coupled to a heat sink111. An isolation foil 112 is arranged between the semiconductorcomponent 100 and the heat sink 111. The isolation foil 112 isconfigured to dissipate heat from the semiconductor component 100 to theheat sink 111. The use of isolation foils 112, however, is usuallyrather expensive. A further drawback of isolation foils 112 is thatadditional process steps are required. This is because the semiconductorcomponent 100, the heat sink 111 and the isolation foil 112 have to bepurchased separately and subsequently have to be assembled by an enduser. The isolation foil 112 is first laminated to the heat sink 111 andthen the semiconductor component 100 is attached to the isolation foil112. The isolation foil 112 may be a ceramic foil, for example. Theisolation foil 112 generally may be electrically non-conductive andthermally conductive.

Generally, the creepage distances in the arrangement in FIG. 1 arerather large. This is schematically illustrated in FIG. 2 whichillustrates a top view of the arrangement of FIG. 1. The creepagedistances are schematically indicated by arrows in FIGS. 1 and 2.

FIG. 3 illustrates another example of a known method for mounting asemiconductor component 100 to a heat sink 111. In the example of FIG.3, the heat sink 111 and the semiconductor component 100 each comprise ahole 121, 122. A screw 120 may be inserted into the holes 121, 122 tofix the semiconductor component 100 to the heat sink 111. A compressionwasher 123 may be inserted between the screw 120 and the semiconductorcomponent 100. This method, however, also has several drawbacks. Forexample, the thermal conductivity depends on a filler material (usuallySilicon) that acts as a thermal dissipator and the resultingSilicon/Resin ratio is usually limited/balanced by the moldabilityperformance. Other mechanical fasteners are known for attaching asemiconductor component 100 to a heat sink 111, including nuts and boltsor spring clips with either greased mica or thermally-enhanced siliconepads, for example.

A further known method is illustrated in FIG. 4. The semiconductorcomponent 100 is mounted on a substrate 130, in particular a directcopper bonded (DCB) substrate 130. The DCB substrate comprises a ceramicdielectric insulator layer 131. Pure copper layers 132 are applied andbonded to the ceramic layer 131 on both sides using great adhesivestrength in a high temperature melting and diffusion process. Thesemiconductor component 100 is then soldered to a first side of the DCBsubstrate 130 using a solder layer 135. The heat sink 111 may be coupledto the second side of the DCB substrate 130 opposite the first surface.A heat spreader 136 may be inserted between the DCB substrate 130 andthe heat sink 111. For example, the DCB substrate 130 may be soldered tothe heat spreader 136 by means of a solder layer 135. A thermal greaselayer 137 may be arranged between the heat spreader 136 and the heatsink 111.

The heat spreader 136 may be a copper baseplate or aluminium baseplate.However, especially in the lower power range, arrangements without abaseplate are also frequently used. In such an arrangement the secondsolder layer 135 and heat spreader 136 may be omitted and the DCBsubstrate 130 may be coupled to the heat sink 111 via the thermal greaselayer 137. Even though an arrangement including a DCB substrate 130 hasseveral advantages such as a high mechanical strength and mechanicalstability, good adhesion and corrosion resistance, and a very goodthermal conductivity, it also has some drawbacks. The drawbacks includehigh costs. Furthermore, several additional process steps are requiredduring assembly of the arrangement and the isolation is rather thick(e.g., minimum of 250 μm).

FIG. 5 illustrates a first exemplary embodiment of a semiconductorcomponent 100 according to the present invention. The semiconductorcomponent 100 comprises a semiconductor package 110. A first thermallyconductive layer 115 is arranged on an outer surface of thesemiconductor package 110. The first thermally conductive layer 115formed on the outer surface of the semiconductor package is configuredto be mounted to an external heat sink 111. Correspondingly, thesemiconductor component 100 with the first thermally conductive layer115 arranged on the outer surface of the semiconductor component 110 isconfigured to be mounted to an external heat sink 111 such that thefirst thermally conductive layer 115 faces the heat sink 111.

A method for producing a semiconductor component 100 comprises forming afirst thermally conductive layer 115 on an outer surface of asemiconductor package 110. The first thermally conductive layer 115formed on the outer surface of the semiconductor package 110 isconfigured to be mounted to an external heat sink 111.

In one example, the semiconductor component 100 includes at least onesemiconductor die 114 (see FIG. 11) that is arranged within thesemiconductor package 110. The first thermally conductive layer 115 maybe arranged on a first outer surface or external surface of thesemiconductor package 110. The first outer surface of the semiconductorpackage 110 may comprise an electrically conductive surface 140 such asa heat sink or exposed die pad (see FIG. 11), for example. Theelectrically conductive surface 140 may comprise an electricallyconductive material such as a metal, for example. The semiconductorpackage 110 may comprise a casing made of plastic, glass or ceramic, forexample. The casing may comprise an opening on one side, e.g. bottomside or top side. The electrically conductive surface 140 may bearranged within this opening such that it forms a part of the respectiveouter surface of the semiconductor package 110.

The semiconductor component 100 may comprise pins or leads 113 (see FIG.11) for mounting the semiconductor component 110 to a printed circuitboard (PCB) or a DCB 200, for example. The pins or leads 113 may beinserted in through holes of a PCB or may be surface mounted to a PCB,for example. The electrically conductive surface 140 of thesemiconductor component 100 may be thermally coupled to an external heatsink 111 by means of the first thermally conductive layer 115. Thismeans that the first thermally conductive layer 115 is arranged betweenthe semiconductor component 100 and the external heat sink 111. Theexternal heat sink 111 may comprise a thermally conductive material andis configured to dissipate heat from the semiconductor component 100.The external heat sink 111 may comprise fins, as is illustrated in FIG.5, to increase the surface area of the external heat sink 111. In thisway, more heat may be delivered to a surrounding medium such as air, orany other suitable cooling fluid (not illustrated in FIG. 5). A heatsink 111 comprising fins, however, is only an example.

The first thermally conductive layer 115 is formed on the semiconductorpackage 110 before the package 110 is mounted to the external heat sink111, in particular before the semiconductor component 100 is sold to afinal customer. The thermally conductive layer 115, together with thesemiconductor component 100, may then be mounted to an external heatsink 111 such that the thermally conductive layer faces the externalheat sink 111 and is arranged between the semiconductor component 100and the external heat sink 111.

The first thermally conductive layer 115 may comprise a ceramicmaterial, for example. However, any other materials may be used, forexample any materials providing sufficient electrical isolation and goodthermal conductivity. As the first thermally conductive layer 115 isformed on the semiconductor component 100 before the semiconductorcomponent 100 is delivered to the end customer, the mounting process forthe end customer becomes much more convenient. The end customer onlyneeds to purchase the semiconductor component 100 with the thermallyconductive layer 115 already applied thereon. The end customer caneasily mount the semiconductor component 100 to the external heat sink111.

The semiconductor package 110 in the example of FIG. 5 may be aso-called TO-220 package. This is, however, only an example. Any otherpackages having an electrically conductive surface such as an exposedheat sink or exposed die pad, for example, arranged at an outer surfaceof the semiconductor package 110 are generally suitable such as DPAK orsplit leadframe packages, for example.

According to one example, a method comprises forming a first thermallyconductive layer 115 on an outer surface of the semiconductor package110. The thermally conductive layer 115 is formed before mounting thesemiconductor package 110 to an external heat sink 111. The thermallyconductive layer 115 formed on the semiconductor package 110 isconfigured to be mounted to an external heat sink 111.

FIG. 6 illustrates a further example of a method for producing asemiconductor component 100. The method may comprise two successivesteps, for example. In a first step, a first material 300 may bedeposited on the electrically conductive surface (e.g., heat sink orexposed die pad) 140 of the semiconductor package 110. The firstmaterial 300 may be or may include boron nitride, in particularhexagonal boron nitride, for example. The first material 300 may be aceramic based material and may include an oxide, carbide or nitridecombination. The first material 300 may include aluminium oxide, siliconcarbide or silicon dioxide, for example. The first material 300 (e.g.,the boron nitride) may be provided in the form of droplets or platelets,for example. The first step may comprise an electrophoretic depositionprocess, for example. Electrophoretic deposition (EPD) is a term usedfor a broad range of industrial processes including electrocoating,cathodic electrodeposition, anodic electrodeposition, electrophoreticcoating and electrophoretic painting, for example. A characteristicfeature of this process is that colloidal particles suspended in aliquid medium migrate under the influence of an electric field(electrophoresis) and are deposited onto an electrode. Generally, allcolloidal particles that can be used to form stable suspensions and thatcan carry a charge can be used in an electrophoretic deposition process.This includes materials such as polymers, pigments, dyes, ceramics andmetals, for example.

The semiconductor package 110 has a semiconductor die 114 arrangedinside. An electrically conductive surface (e.g., heat sink or exposeddie pad) 140 at least partially forms one of the outer surfaces of thesemiconductor package 110. The electrically conductive surface 140 iselectrically coupled to at least one pin or lead 113. The at least onepin or lead 113 is configured to electrically contact the semiconductordie 114 within the semiconductor package 110 and to electrically couplethe semiconductor die 114 to any surrounding circuitry and any othercomponents that may be arranged on the same printed circuit board, forexample. The electrical connection between the pin or lead 113 and theelectrically conductive surface 140 may be formed via the semiconductordie 114 within the semiconductor package 110.

The at least one pin or lead 113 may be coupled to a power supply so asto apply a direct current to the electrically conductive surface 140 ofthe semiconductor package 110. In one example, a voltage of between 1and 1000V is applied to the electrically conductive surface 140. Thesemiconductor component 100 may be submerged into a container or vessel,for example, which holds the coating bath or solution. One or moreso-called counter-electrodes may be used to complete the circuit (notillustrated in FIG. 6).

The general principle of an arrangement for electrophoretic depositionis schematically illustrated in FIG. 7. The arrangement comprises acontainer or vessel 410. A coating bath or solution is held in thecontainer or vessel 410. The electrically conductive surface 140 that isto be coated as well as at least one counter-electrode 150, are immersedinto the coating bath or solution within the container 410. Theelectrically conductive surface 140 and the counter-electrode 150 areeach connected to terminals, namely a terminal for providing a positivepotential and a terminal for providing a negative potential,respectively. For example, if the electrically conductive surface 140 iscoupled to a terminal for a negative potential (−), thecounter-electrode 150 is coupled to a terminal for a positive potential(+), as is illustrated in FIG. 7, or vice versa. During the EPD process,a direct current is applied to the electrically conductive surface 140and to the counter-electrode 150, and, therefore, also to the solutionor colloidal suspension within the container 410. The solution orcolloidal suspension may comprise ionizable groups.

There are generally two different types of E102PD processes, namelyanodic and cathodic. In the anodic process, negatively charged materialis deposited on the positively charged electrode, or anode. In thecathodic process, positively charged material is deposited on thenegatively charged electrode, or cathode. When an electric field isapplied, the charged particles within the solution or suspension migrateby the process of electrophoresis towards the electrode with theopposite charge. There are several mechanisms by which the material canbe deposited on the electrode, including charge destruction and theresultant decrease in solubility, concentration coagulation, and saltingout, for example. Such EPD processes are generally known in the art andwill not be described in further detail herein. The so-calleddipping-method of FIG. 7 is further exemplarily illustrated in FIG. 8.

FIG. 8 illustrates a semiconductor component 100 with a semiconductorpackage 110 that is immersed into the solution or suspension 411 in thecontainer 410. Although the arrow in FIG. 8 indicates that thesemiconductor component 100 is being immersed into the solution 411, afirst layer 320 is illustrated on an outer surface of the semiconductorpackage 110. The first layer 320 may be formed on an electricallyconductive surface of the semiconductor component 100 during the EPDprocess.

Again referring to FIG. 6, a first layer 320 is formed on the outersurface of the semiconductor package 110 by depositing the firstmaterial 300 and, after depositing the first material 300, in a secondstep depositing a second material 310 on the first material 300 or on apre-layer formed by the first material 300. The second material 310 maybe a thermally conductive material with or without fillers. For example,the second material 310 may be or may include a polymer. The polymer maybe an epoxy or a silicon based polymer. The polymeric material may be asoft polymeric material (flexible type polymer) or the polymericmaterial may be hardened. The second material 310 may be provided in theform of droplets or platelets, for example. The second step may comprisean electrophoretic deposition process, as has been described above withrespect to the first step, or a dispensing method, for example.

The general principle of such a dispensing method is schematicallyillustrated in FIG. 9. Instead of a dispensing method as is illustratedin FIG. 9, an electrostatic spraying method may be used, for example.During a dispensing or electrostatic spraying method, a liquid flowemerging from a tip or thin tube 400 under the influence of a strongelectric field breaks up into small droplets due to a charging of thedielectric liquid. If a polymer material is dissolved in the liquid,this technique may be utilized to produce a polymer layer on anelectrode. In the example of FIG. 9, the electrode is formed by theelectrically conductive surface 140 with the first pre-layer 320 (formedin step 1) deposited thereon. As has been described with reference toFIG. 6, the at least one pin or lead 113 of the semiconductor component100 may be coupled to a power supply. Instead of a wet solution that isbroken up into small droplets, it is also possible to apply a dry powderincluding the second material 310, for example a polymer, to the firstmaterial 300 or the first pre-layer. The particles in the dry powder maybe electrically charged and may be attracted by the electricallyconductive surface 140 when coupled to a power supply. The chargedparticles in the liquid or the powder are initially projected towardsthe electrically conductive surface 140 and may be accelerated towardsthe electrically conductive surface 140 by an electrostatic chargeprovided by the power supply. Depending on the charge of the particles,the electrically conductive surface 140 may be coupled to the positive(negatively charged particles) or the negative terminal (positivelycharged particles) of the power supply.

A polymer may alternatively be deposited on the electrically conductivesurface 140 using a polymer coating process or so-called e-coatingmethod. Polymer coating processes generally include extrusion/dispersioncoating or solution application techniques, for example. E-coatingmethods include immersing the electrically conductive surface in a baththat consists of a water-based solution, for example. An electriccurrent is then used to attract the particles that are suspended in theliquid solution and deposit them onto the surface of the substrate. Thee-coating, therefore, is very similar to the electrophoretic deposition.

After completing the second step, the first layer 320 includes both thefirst material 300 and the second material 310. In some examples thefirst step is followed by a sintering process before performing thesecond step. Such a sintering process, however, is optional. Sinteringgenerally is the process of compacting and forming a solid mass ofmaterial by applying heat or pressure, without melting the material tothe point of liquefaction. The sintering may enhance properties such asstrength and thermal conductivity, for example. If the first materialincludes ceramic, the sintering process at a high temperature may fusethe ceramic particles together.

Referring to FIG. 10, an example of a method for producing asemiconductor component 100 is illustrated. In a first step, illustratedin FIG. 10A, a first material 300 is deposited on an electricallyconductive surface 140. The first step may comprise an electrophoreticdeposition process, as has been described with respect to FIG. 6. Anoptional sintering step may follow (not illustrated in FIG. 10). In asecond step, illustrated in FIG. 10B, a second material 310 is depositedon the first material 300 already arranged on the electricallyconductive surface 140. The second step may comprise an electrophoreticdeposition process or a dispensing method, as has been described withrespect to FIG. 6 above. The second material 310 may be deposited on thesurface of a pre-layer that is formed by the first material 300.However, as this pre-layer includes droplets or platelets of the firstmaterial 300, the pre-layer may be porous with empty spaces or cavitiesbetween the separate droplets or platelets (as illustrated in FIG. 10A),the second material 310 may at least partially fill the empty spaces orcavities of the porous pre-layer between the droplets or platelets ofthe first material 300, as is schematically illustrated in FIG. 10B.

The first material 300 may be or may include hexagonal boron nitride.The deposited first material 300 may form a hexagonal boron nitridepre-layer on the electrically conductive surface 140. The secondmaterial 310 may be or may include a polymer and may form a polymercoating on the first material 300. The resulting first layer 320comprises the first material 300 as well as the second material 310. Thesecond step may optionally be followed by a third step during which thefirst layer 320 comprising the first material 300 and the secondmaterial 310 is exposed to a vacuum and/or high temperatures. Thetemperatures may be room temperature (typically between 20° C. and 25°C.), up to 100° C., up to 150° C., up to 200° C. or up to 500° C., forexample. The third step is exemplarily illustrated in FIG. 10C. Whileheating and/or exposing the first layer 320 to a vacuum, the first layer320 may be polymerized. Generally, during polymerization monomermolecules are reacted together in a chemical reaction to form polymerchains or three-dimensional networks. There are generally many forms ofpolymerization. During this third polymerization step, the firstmaterial 300 (e.g., hexagonal boron nitride) may be crosslinked with thesecond material 310 (e.g., polymer). The first material 300 may be, soto speak, held in place by the second material 310. The structure of thefirst material 300 and/or the second material 310 may be altered duringthe third step, as is schematically illustrated in FIG. 10C. Inparticular, the connections between the first material 300 and thesecond material 310 may be altered. This may provide very goodmechanical properties to the first layer 320.

The first layer 320 may have a mass fraction of >90 wt % and provide adense layer 320 of boron nitride and polymer on the electricallyconductive surface 140. When high temperatures are used, a sinteredboron nitride layer may be formed on the electrically conductive surface140. The suspension that is used during the first electrophoreticdeposition process may be water based, and may include a binder (e.g.,cationic binder, anionic binder or uncharged binder) on a 0.1-60 wt % BNweight basis, for example. The electropohoretic deposition process usingan aqueous based solution for depositing a hexagonal boron nitridefiller on the electrically conductive surface 140 may be followed by apolymer coating step. For example, a method may comprise an EPD(electropohoretic deposition process) boron nitride deposition followedby (i) conformal coating (dispensing or dipping), (ii) e-coating, or(iii) sintering. If options (i) or (ii) are used, an electricallyisolating but thermally conductive (ceramic) layer may be formed on theelectrically conductive surface 140. If option (iii) is used, a sensorcoating, corrosion protection and/or mould realizing coating may beformed on the thermally conductive surface 140.

The thickness of an electrically non-conducting thin ceramic layer ofhexagonal boron nitride may be in the range of about 1-20 μm, 20-40 μm,40-100 μm or 100-300 μm, for example. A ceramic layer of hexagonal boronnitride of such a thickness may provide electrical isolation forvoltages from about 0.1-10 kV/s. Generally, the electrical isolationdepends on the thickness of the first material 300 (e.g., ceramic)deposited on the outer surface of the semiconductor, the first material300 being coated by the second material 310 (e.g., polymer). A thermalconductivity of about 2 W/mK, 10 W/mK or 20 W/mK may be achieved withthe proposed solution, for example.

FIG. 12 (FIGS. 12A-12G) shows a method for forming a matrix compositelayer on a heat sink according to an embodiment.

In a first step, illustrated in FIG. 12A, a heat sink 111 is provided.The heat sink 111 may be embedded in an encapsulation material of apackage 210. The heatsink 111 may comprise a heat sink metal such ascopper, nickel, tin, gold etc. The encapsulation material of the package210 may include plastic, glass or ceramic, etc. In the next step,illustrated in FIG. 12B, a top surface 181 of the heat sink 111 isroughened so that the previously smooth surface of the heat sink 111 isnow rough. Rough means that the surface of the heat sink includes smallirregular notches, recesses or indents 182. The top surface 181 may havea roughness of less than 1 μm (R_(a)<1 (or alternatively R_(a)<1.5, <2,<3 or <5), i.e., the arithmetical mean height is less than 1 μm. Thesurface roughness may be, however, larger than 0.025 (R_(a)>0.03, >0.05or >0.1).

In the next step, illustrated in FIG. 12C, a dam or wall 220 is formedor attached around the heat sink surface or a package 210 (embedding theheat sink) 181. The dam 220 may be placed around the perimeter and/orcircumference of the heat sink 111. The dam 220 may be placed on thepackage 210 as shown in FIG. 12C making the entire top surface 181 ofthe heatsink 111 (and maybe portions of the top surface of the package210) available for deposition or dispense of the filler and plasticmaterials. The dam 220 is used for containing the later deposited ordispensed materials. The dam 220 may be placed only on (portions) of thetop surface 211 of the package 210 material or on the (portion) of thetop surface 211 of the package 210 and a portion of the top surface 181of the heat sink 111. The dam 220 may be placed directly next to theperimeter of the heat sink 111 or may be laterally spaced apart from theperimeter of the heat sink 111 on the top surface 211 of the package 210(as shown in, e.g., FIG. 15A). The dam 220 may comprise a crosslinkingmaterial such as an epoxy material or a polymer material. In variousembodiments, the dam may include silicon, acrylic, etc. The crosslinkingmaterial of the dam and the plastic material 350 may be the samematerial or a different material.

The dam 220 may be pre-formed and adhered to the heat sink 111/package210. Alternatively, the epoxy or polymer material is dispensed and thencrosslinked by ambient temperature, heat or ultraviolet light (UV)light. The dam 220 may be about 220 μm high. Alternatively, the dam mayhave a high of 200 μm to 250 μm, 10 μm to 300 μm or 100 μm to 500 μm.The height of the dam 220 may depend on the height of the matrixcomposite layer to be deposited or dispensed.

FIG. 12D shows a top view of the heat sink 111 with the dam 220. In thisparticular example, the dam 220 is placed around the perimeter of theheatsink 111 and around the circumference of the inner hole 183. The dam220 around the perimeter and the circumference of the inner hole 183 mayinclude the same thickness and the same height. Alternatively, the dam220 may comprise different thicknesses and/or heights.

In the next step, illustrated in FIG. 12E, a first material 340 such asa filler material is formed on the roughened surface 181 of the heatsink 111 within the and bordered by the dam 220. The filler material 340may be a ceramic material. The ceramic material may include nitride,oxide and a carbide base material. The ceramic material may include(hexagonal) boron nitride, alumina oxide or alumina nitride, boroncarbide. The filler material may be the same as previously disclosed.The deposition method may a dispensing method wherein the fillermaterial 340 is dispensed by a dispenser. Alternatively, the same orsimilar deposition methods as previously disclosed can be used. Thefiller material 340 may be ceramic filler with or without surfacecoating. The filler material 340 (e.g., ceramic filler material) may bepretreated so that it can crosslink with a polymer. The filler material340 is filled up to the height of the dam 220 or to a height lower thanthat of the dam 220.

In the next step, illustrated in FIG. 12F, a second material 350 such asa plastic material is deposited or formed on the filler material 340.The plastic material 350 may a crosslinking material such an epoxymaterial or a polymer material. Alternatively, the plastic material 350may be the same as previously disclosed. In various embodiments, thecrosslinking material 350 may be a silicone or an acrylic. Thedeposition method may a dispensing method wherein the plastic material350 is dispensed by a dispenser. Alternatively, the same or similardeposition methods as previously disclosed can be used. The plasticmaterial 350 may be the same or may be different to the material usedfor the dam 220.

Then, a matrix composite layer 360 is formed by exposing the fillermaterial 340 and the plastic material 350 to vacuum/and or temperatureso that the matrix composite layer 360 is formed on the roughened heatsink surface 181. The material depositions 340/350 may be cured at roomtemperature or at a higher temperature. A high or higher temperature canbe a temperature in the temperature ranges of 80° C. to 120° C., 100° C.to 150° C. or 120° C. to 200° C. The material depositions 340/350 may beexposed to vacuum. Typical vacuum level ranges are provided in thefollowing table:

Vacuum Level Ranges Atmospheric Pressure 760 Torr Low Vacuum (Rough) 760to 25 Torr Medium Vacuum (Rough) 25 to 1 × 10⁻³ Torr High Vacuum (Hard)1 × 10⁻³ to 1 × 10⁻⁹ Torr

The matrix composite layer 360 disposed on the heat sink 111, is shownin FIG. 12G. The dam 220 may remain on the heat sink 111.

Alternatively, the exposure to vacuum may not be performed as a separateadditional step after depositing the filler and plastic materials 340,350 (FIGS. 12E and 12F) but rather while the filler material and theepoxy material are deposited. The temperature may be applied duringthese steps (together with the exposure to vacuum) or separatelyafterwards. The exposure to vacuum may remove air bubbles and/or otherchemical additives. It is advantageous to form the matrix compositelayer 360 on a roughened heat sink surface because it adheres andconnects better to the heat sink 111.

FIG. 13 (FIGS. 13A-13G) shows a method for forming a matrix compositelayer on a heat sink according to another embodiment.

The method of FIG. 13 is the same as the one in FIG. 12 with theexception of an additional step inserted between method steps FIGS.12C/13C and 12E/13E. Accordingly, FIGS. 13A-13C show roughening the heatsink surface 181 and building a dam 220 around the perimeter and/or thecircumference of the heat sink 111/package 210.

After building the dam 220, a third material 370 such a (plastic)crosslinking material, e.g., an epoxy material or a polymer material(crosslinking polymer material) is deposited or dispensed within theperimeter/circumference of or inside the dam 220. The third material 370is dispensed in order to cover the rough surface 181 of the heat sink111. This is shown in FIG. 13D. This is advantageous because it providesa (air) bubble free rough top surface 181 and provides good adhesion forthe matrix composite layer 360. The crosslinking material 370 may alsobe a silicone or an acrylic. The deposition method may be a dispensingmethod wherein the third material 370 is dispensed by a dispenser.Alternatively, the same or similar deposition methods as previouslydisclosed can be used. The third material 370 may be dispensed up to aheight 1 μm to 10 μm or, alternatively, 0.5μ to 5 μm.

In the next steps, illustrated in FIGS. 13E-13G, the filler material 340and the plastic material 350 are deposited (e.g., dispensed) and thematrix composite layer 380 is formed similar to the method disclosed inFIGS. 12E-12G. Again, the deposition (e.g., dispense) of the filler andplastic materials 340, 350 can be performed under vacuum conditions orthe deposited layer can be exposed to a vacuum and/or temperature afterthey are deposited. The third material 370, the plastic material 350 andthe crosslinking material of the dam 220 may comprise the same materialsor different materials.

FIG. 14 (FIGS. 14A-14E) shows a method for forming a matrix compositelayer on a heat sink according to yet another embodiment.

In a first step, illustrated in FIG. 14A, a roughened heat sink 111 isprovided. The heat sink 111 may be embedded in an encapsulation materialof the package 210. The heatsink 111 may comprise a heat sink metal suchas copper, nickel, tin, gold, etc. The encapsulation material of thepackage 210 may include plastic, glass or ceramic, etc. The heat sink111 may be roughened according to a procedure discussed in FIG. 12B.

In the next step, illustrated in FIG. 14B, a clamper 390 such as a sidewall clamper grabs or grasps the heatsink 111 or clamps to the package210 surrounding the heat sink 111. The clamper 390 may grab, grasp orclamp to the heat sink 111 at a sidewall of the heat sink 111 or at thesidewall of the package 210. The clamper 390 may be a jig clamper(prefix jig from side or top package to create required shape). Otherclampers 390 may be used. The clamper 390 may grab or grasps the heatsink/package 111/210 in an angle between equal or more than 3° degreeand equal or less than 100°. Alternatively, the clamper 390 may grab orgrasps the heat sink/package 111/210 in an angle between equal or morethan 5° degree and equal or less than 15°. Clamping the heatsink/package 111/210 with an angle is advantageous because the clamper390 can be easier released compared to a clamper having not such anangle.

The clamper 390 may clamp to the outer sidewall and the inner hole 183of the heat sink/package 111/210 at the same time so that so that wallsare formed similar to that of the dam 210. The clamper 390 is used forcontaining the later deposited or dispensed materials. In the nextsteps, illustrated in FIGS. 14C-14E, the filler material 340 and theplastic material 350 deposited (e.g., dispensed) and the matrixcomposite layer 360/380 is formed similar to the method disclosed inFIGS. 12E-12G. Again, the deposition (e.g., dispensing) of the fillerand plastic materials 340/350 can be performed under vacuum conditionsor the deposited (e.g., dispensed) layers can be exposed to vacuumand/or temperature after they are deposited. In a further variation, anepoxy material 370 can be deposited similar to that shown in FIG. 13D.

FIGS. 15A-15D show different types of filler materials in the matrixcomposite layer disposed on the heat sink.

FIGS. 15A and 15B illustrate matrix composite layers 385/386 disposed onthe heat sink 111, wherein the filler materials 355/356 compriseindividual spherical filler particles or individual platelet fillerparticles (e.g., ceramic particles). The filler particles may becircular or oval, ball shaped or ellipsoid. Alternatively, the filerparticles may be a polygon platelet or a three dimensional polygon. Thefiller particles 355 may comprise substantially the same size as shownin FIG. 15A or different sizes as shown in FIG. 15B. The particles maybe aligned in specific direction, or randomly or irregularly distributed(no main direction). For example, FIG. 15A shows oval or ellipsoidparticles 355 having the substantially the same size aligned with theirmain direction parallel to the top surface 181 of the heat sink 111. Incontrast, FIG. 15B shows ball shaped/circular and ellipsoid/ovalparticles 356 of different sizes randomly distributed with no particularpreferred alignment.

FIG. 15C illustrates a matrix composite layer 387 having a fillermaterial 357 of agglomerated spherical/platelet filler particles (e.g.,ceramic particles). The agglomerated particles 357 may be disposed suchthat their main direction is aligned and that they are aligned sphere orround shape to the top surface 181 of the heat sink 111. Again, theagglomerated particles 357 themselves may comprise substantially thesame size or different size. Similarly, the particles in theagglomerated particles 357 may comprise substantially the same size ordifferent sizes.

FIG. 15D illustrates a matrix composite layer 388 having agglomeratedspherical/platelet filler particles 357 (e.g., ceramic particles) andindividual filler particles 355/356. Any combination of these differentparticles is possible. For example, aligned individual filler particlescan be combined with aligned agglomerated filler particles (e.g.,aligned orthogonal to each other), aligned agglomerated filler particlescan be combined randomly distributed individual filler particles(having, e.g., the same or different sizes), etc. The agglomeratedfiller particles 357 may be disposed on certain regions 391 on thesurface 181 of the heat sink 111 and the individual filler particles355/356 may be disposed on other regions 392 of the surface 181 of theheat sink 111. By providing the agglomerated filler particles 357 incertain regions 391 and the individual filler particles 355/356 in otherregions 392 the thermal conductivity and/or the electrical insolation ofthe matrix composite layer 388 can be configured. For example, thethermal conductivity and/or electrical isolation of the matrix compositelayer 388 in the regions 392 where the individual filler particles355/356 are disposed may be higher than the thermal conductivity of thematrix composite layer 388 in regions 391 where the agglomeratedparticles 357 are located (or vice versa). Alternatively, the thermalconductivity and/or electrical isolation of the matrix composite layer388 in the regions 392 where the filler particles are aligned 355 may behigher than the thermal conductivity and/or electrical isolation of thematrix composite layer 388 in regions 392 where the filler particles 355are not aligned (or vice versa). Accordingly, the matrix composite layer388 can be configures or arranged such that the regions where a package110 is attached to the heat sink 111 has a high thermal conductivity anda high electrical isolation while areas where no package is attached tothe heat sink 111 has a high thermal conductivity and an electricallyconductive, for example.

In various embodiments, the embodiment methods for forming a matrixcomposite layer on a heat sink 111 can also be performed to form amatrix composite layer on the heat sink 140 of the package 110.

In various further embodiments, the matrix composite layer is a layerwith a high filler content. For example, the filler content may be equalor more than 30 wt %, equal or more than 80 wt %, equal or more than 900wt %, or equal or more than 95 wt %.

In various other embodiments, the electrical isolation of the matrixcomposite layer depends on the thickness of the layer, i.e., the thickerthe layer the better the electrical isolation.

The following embodiments and aspects of the disclosure and can becombined in all possible combinations and permutations.

In a first embodiment a method includes forming a wall around a metallicsurface such that the wall extends in a vertical direction from a planeformed by the metallic surface of a workpiece, depositing a fillermaterial in a walled area on the metallic surface, depositing a plasticmaterial on the filler material and performing a vacuum treatment of thefiller material and the plastic material thereby forming a matrixcomposite layer disposed on the metallic surface.

According to a first aspect of this embodiment the vacuum treatment isperformed after the filler material and the plastic material aredeposited.

According to a second aspect of this embodiment the vacuum treatment isperformed while the filler material and the plastic material aredeposited.

According to a third aspect of this embodiment depositing the fillermaterial comprises dispensing the filler material, and depositing theplastic material comprises dispensing the plastic material.

According to a fourth aspect of this embodiment the metallic surfacecomprises a roughened metallic surface, and a crosslinking material isdirectly formed on the roughened metallic surface of the workpiecebefore the filler and plastic materials are deposited.

According to a fifth aspect of this embodiment the matrix compositelayer comprises a filler content of equal or more than 90 wt %.

According to a sixth aspect of this embodiment the plastic material is acrosslinking material, and the filler material is a ceramic fillermaterial.

According to a seventh aspect of this embodiment the ceramic fillermaterial comprises nitride or oxide, and a carbide base material.

According to an eighth aspect of this embodiment the filler materialcomprises two or three dimensional particles, platelets, agglomeratedparticles or a combination thereof.

According to a ninth aspect of this embodiment the workpiece is a heatsink.

In a second embodiment a method includes clamping sidewalls of aworkpiece with a clamper, depositing a filler material on a metallicsurface of the workpiece, depositing a plastic material on the fillermaterial and performing a vacuum treatment of the filler material andthe plastic material thereby forming a matrix composite layer disposedon the metallic surface.

According to a first aspect of this embodiment the vacuum treatment isperformed after the filler material and the plastic material aredeposited.

According to a second aspect of this embodiment the vacuum treatment isperformed while the filler material and the plastic material aredeposited.

According to a third aspect of this embodiment depositing the fillermaterial comprises dispensing the filler material, and depositing theplastic material comprises dispensing the plastic material.

According to a fourth aspect of this embodiment the metallic surface isa roughened metallic surface, and a crosslinking material is directlydeposited on the roughened metallic surface of the workpiece before thefiller and plastic materials are deposited.

According to a fifth aspect of this embodiment the matrix compositelayer comprises a filler content of equal or more than 90 wt %.

According to a sixth aspect of this embodiment the plastic material is across linking material and the filler material is a ceramic fillermaterial.

According to a seventh aspect of this embodiment the ceramic fillermaterial comprises nitride or oxide, and a carbide base material.

According to a eighth aspect of this embodiment the filler materialcomprises three dimensional particles, platelets, agglomerated particlesor a combination thereof.

According to a ninth aspect of this embodiment the workpiece is a heatsink.

In a third embodiment an arrangement includes a heatsink with aroughened metallic surface and a matrix composite layer disposed on theroughened metallic surface, wherein the matrix composite layer comprisesa ceramic filler material and a plastic material, and wherein theceramic filler material includes two or three dimensional particles,platelets, agglomerated particles or a combination thereof.

In a fourth embodiment a method includes forming a first thermallyconductive layer on an outer surface of a semiconductor package, whereinforming the first thermally conductive layer comprises depositing afirst material on the outer surface of the semiconductor package; anddepositing a second material on the first material after depositing thefirst material.

According to a first aspect of this embodiment forming the firstthermally conductive layer comprises an electrophoretic depositionprocess.

According to a second aspect of this embodiment depositing the firstmaterial comprises forming a porous pre-layer on the outer surface ofthe semiconductor package.

According to a third aspect of this embodiment the porous pre-layercomprises cavities and depositing the second material on the firstmaterial comprises at least partially filling the cavities of thepre-layer.

According to a fourth aspect of this embodiment depositing the firstmaterial comprises an electrophoretic deposition process.

According to a fifth aspect of this embodiment the first materialcomprises at least one of the following: boron nitride, aluminium oxide,silicon carbide, silicon dioxide, or a ceramic material including anoxide or nitride combination.

According to a sixth aspect of this embodiment depositing the secondmaterial on the first material comprises at least one of anelectrophoretic deposition process, an e-coating process, a dispensingmethod, an electrostatic spraying method or a dipping method.

According to a seventh aspect of this embodiment the second materialcomprises a thermally conductive material with or without fillers or apolymer.

According to a eighth aspect of this embodiment the method furtherincludes, after depositing the first material, sintering the firstmaterial.

According to a ninth aspect of this embodiment, after depositing thesecond material, the method further comprises at least one of: heatingthe first and the second material; or exposing the first and the secondmaterial to a vacuum.

According to a tenth aspect of this embodiment the first materialdeposited on the outer surface of the semiconductor package has a firstthickness, and the thermal conductivity of the first thermallyconductive layer is dependent on the first thickness.

According to a eleventh aspect of this embodiment the outer surface ofthe semiconductor package comprises an electrically conductive surface.

According to a twelfth aspect of this embodiment the electricallyconductive surface is a heat sink or a die pad of the semiconductorpackage.

According to a thirteenth aspect of this embodiment forming the firstthermally conductive layer comprises applying a direct current to theelectrically conductive surface.

According to a fourteenth aspect of this embodiment the first thermallyconductive layer formed on the outer surface of the semiconductorpackage is configured to be mounted to an external heat sink.

In a fifth embodiment a semiconductor component includes a semiconductorpackage with an outer surface and a first thermally conductive layerarranged on the outer surface of the semiconductor package, wherein thefirst thermally conductive layer comprises a first material comprising aporous pre-layer disposed on the outer surface of the semiconductorpackage and a second material disposed over first material.

According to a first aspect of this embodiment the first materialcomprises at least one of the following: boron nitride, aluminium oxide,silicon carbide, silicon dioxide, or a ceramic material including anoxide or a nitride combination.

According to a second aspect of this embodiment the second materialcomprises: a thermally conductive material with or without fillers or apolymer.

According to a third aspect of this embodiment the outer surfacecomprises an electrically conductive surface.

According to a fourth aspect of this embodiment the electricallyconductive surface is a heat sink or a die pad of the semiconductorcomponent.

According to a fifth aspect of this embodiment the semiconductorcomponent with the first thermally conductive layer arranged thereon isconfigured to be mounted to an external heat sink such that the firstthermally conductive layer faces the external heat sink.

According to a sixth aspect of this embodiment the porous pre-layercomprises cavities and the second material at least partially fills thecavities of the porous pre-layer.

Although various exemplary embodiments of the invention have beendisclosed, it will be apparent to those skilled in the art that variouschanges and modifications can be made which will achieve some of theadvantages of the invention without departing from the spirit and scopeof the invention. It will be obvious to those reasonably skilled in theart that other components performing the same functions may be suitablysubstituted. It should be mentioned that features explained withreference to a specific figure may be combined with features of otherfigures, even in those cases in which this has not explicitly beenmentioned. Further, the methods of the invention may be achieved ineither all software implementations, using the appropriate processorinstructions, or in hybrid implementations that utilize a combination ofhardware logic and software logic to achieve the same results. Suchmodifications to the inventive concept are intended to be covered by theappended claims.

Spatially relative terms such as “under,” “below,” “lower,” “over,”“upper” and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto those depicted in the figures. Further, terms such as “first,”“second” and the like, are also used to describe various elements,regions, sections, etc. and are also not intended to be limiting. Liketerms refer to like elements throughout the description.

As used herein, the terms “having,” “containing,” “including,”“comprising” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a,” “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

With the above range of variations and applications in mind, it shouldbe understood that the present invention is not limited by the foregoingdescription, nor is it limited by the accompanying drawings. Instead,the present invention is limited only by the following claims and theirlegal equivalents.

What is claimed is:
 1. A method comprising: forming a wall around ametallic surface such that the wall extends in a vertical direction froma plane formed by the metallic surface of a workpiece; depositing afiller material in a walled area on the metallic surface; depositing aplastic material on the filler material; and performing a vacuumtreatment of the filler material and the plastic material therebyforming a matrix composite layer disposed on the metallic surface. 2.The method of claim 1, wherein the vacuum treatment is performed afterthe filler material and the plastic material are deposited.
 3. Themethod of claim 1, wherein the vacuum treatment is performed while thefiller material and the plastic material are deposited.
 4. The method ofclaim 1, wherein depositing the filler material comprises dispensing thefiller material, and wherein depositing the plastic material comprisesdispensing the plastic material.
 5. The method of claim 1, wherein themetallic surface comprises a roughened metallic surface, and wherein acrosslinking material is directly formed on the roughened metallicsurface of the workpiece before the filler and plastic materials aredeposited.
 6. The method of claim 1, wherein the matrix composite layercomprises a filler content of equal or more than 90 wt %.
 7. The methodof claim 1, wherein the plastic material is a crosslinking material, andwherein the filler material is a ceramic filler material.
 8. The methodof claim 1, wherein the filler material comprises two or threedimensional particles, platelets, agglomerated particles or acombination thereof.
 9. The method of claim 1, wherein the workpiece isa heat sink.
 10. The method of claim 7, wherein the ceramic fillermaterial comprises nitride or oxide, and a carbide base material.
 11. Amethod comprising: clamping sidewalls of a workpiece with a clamper;depositing a filler material on a metallic surface of the workpiece;depositing a plastic material on the filler material; and performing avacuum treatment of the filler material and the plastic material therebyforming a matrix composite layer disposed on the metallic surface. 12.The method of claim 11, wherein the vacuum treatment is performed afterthe filler material and the plastic material are deposited.
 13. Themethod of claim 11, wherein the vacuum treatment is performed while thefiller material and the plastic material are deposited.
 14. The methodof claim 11, wherein depositing the filler material comprises dispensingthe filler material, and wherein depositing the plastic materialcomprises dispensing the plastic material.
 15. The method of claim 11,wherein the metallic surface is a roughened metallic surface, andwherein a crosslinking material is directly deposited on the roughenedmetallic surface of the workpiece before the filler and plasticmaterials are deposited.
 16. The method of claim 11, wherein the matrixcomposite layer comprises a filler content of equal or more than 90 wt%.
 17. The method of claim 11, wherein the plastic material is a crosslinking material, and wherein the filler material is a ceramic fillermaterial.
 18. The method of claim 11, wherein the filler materialcomprises three dimensional particles, platelets, agglomerated particlesor a combination thereof.
 19. The method of claim 11, wherein theworkpiece is a heat sink.
 20. The method of claim 17, wherein theceramic filler material comprises nitride or oxide, and a carbide basematerial.
 21. An arrangement comprising: a heatsink with a roughenedmetallic surface; a first dam disposed on an outer perimeter of theheatsink; and a matrix composite layer disposed on the roughenedmetallic surface and contained by the first dam, wherein the matrixcomposite layer comprises a ceramic filler material and a plasticmaterial, and wherein the ceramic filler material includes two or threedimensional particles, platelets, agglomerated particles or acombination thereof.
 22. The arrangement of claim 21, further comprisinga package embedding the heatsink, wherein the first dam is disposed onthe package.
 23. The arrangement of claim 22, wherein the first dam isdisposed on the package and spaced apart from the heatsink.
 24. Thearrangement of claim 21, wherein the first dam comprises an epoxymaterial, a polymer material, silicone or acrylic.
 25. The arrangementof claim 21, wherein the first dam is a preformed dam and adhesivelyconnected to the heatsink.
 26. The arrangement of claim 21, furthercomprising a second dam disposed on the heatsink within the first dam,wherein the matrix composite layer is contained by the first dam and thesecond dam.
 27. The arrangement of claim 21, wherein the first dam has afirst height, wherein the matrix composite layer has a second height,and wherein the second height is smaller or equal than the first height.28. The arrangement of claim 21, further comprising a further materialdirectly disposed on the heatsink and covering the roughened metallicsurface of the heatsink.
 29. The arrangement of claim 21, wherein thematrix composite layer comprises a first region with individual fillerparticles and a second region with agglomerated particles.
 30. Thearrangement of claim 29, wherein the individual filler particles areparticles of different sizes.